Re: Optimizer items in the release notes

On Sat, Apr 27, 2019 at 02:47:44PM +1200, David Rowley wrote:
> On Sat, 27 Apr 2019 at 14:22, Bruce Momjian <bruce(at)momjian(dot)us> wrote:
> > > > * They are hard to explain
> > >
> > > That can be true, but we generally get there if not the first time
> > > then after a few iterations. Authors and committers of the
> > > improvements are likely to be able to help find suitable wording.
> >
> > It is not the text that is hard, but hard to explain the concept in a
> > way that relates to anything a normal user is familiar with.
>
> Yeah, that's no doubt often going to be a struggle, but we can't
> expect every person who reads the release notes to understand
> everything. You could probably say the same for any internal
> implementation change we make though. I don't think the planner is
> unique in this regard, so I don't think it needs any special

I do believe the planner is unique in this regard in the sense that the
changes can make 100x difference in performance, and it is often unclear
from the user interface exactly what is happening.

> treatment. I also don't think we need to go into great detail. The
> item could be as light on detail as:
>
> * Improve query planner's ability to push LIMIT through Sort nodes.
>
> If you don't know what LIMIT is or what a Sort node is, then you're
> probably not going to care about the change. They can keep reading on
> the next line, but if the reader happens to have suffered some pain on
> that during their migration attempt, then they might be quite happy to
> see those words. If they want more details then they might be savvy
> enough to hunt those down, or perhaps they'll come asking.

Uh, that is not clear to me so I am not sure the average user would know
about it. I would probably try to explain that one in a way that can be
understood, like LIMIT in subqueries affecting the outer query sort
performance.

--
Bruce Momjian <bruce(at)momjian(dot)us> http://momjian.us
EnterpriseDB http://enterprisedb.com

+ As you are, so once was I. As I am, so you will be. +
+ Ancient Roman grave inscription +